The present invention relates to an operating mechanism of a transfer unit including a first and a second shift rods which are parallel with each other and axially slidably supported in a transfer case, a drive condition changeover first shift fork on the first shift rod which is shiftable between two wheels drive position and four wheels drive position, a high-neutral-low speed changeover second shift fork on the second shift rod which is shiftable between high speed, neutral and low speed positions, said shift rods having recesses corresponding to said shift positions and engageable with check balls to retain respective positions, one other recess formed on each surface of each shift rod and opposing with each other when the first shift rod is shifted to the four wheels drive position and the second shift rod is shifted to the high speed position, an interlock pin disposed between said opposing surfaces of the shift rods and extending between one surface of one shift rod and one of the other recesses of the other shift rod, said shift rods being selectively shiftable to attain any one of the high speed two wheels drive, high speed four wheels drive, neutral and low speed four wheels drive conditions.
Generally, such a transfer unit receives power from a vehicle-mounted engine through a conventional transmission mechanism and transmits the power to two wheels or to four wheels of the vehicle in a high speed or a low speed driving condition.
Conventional transfer unit of the above-mentioned type has an operating lever to effect changeover between high speed, neutral and low speed drive conditions, and another operating lever to effect changeover between two wheels and four wheels driving conditions. However, to drive such a vehicle, the driver must operate three operating levers including a shift operating lever for the transmission mechanism. Needless to say, such an operation is troublesome.
Japanese Utility Model Application Publication No. 42,495/75 discloses a transfer operating mechanism which has a sole operating lever to perform the two changeover functions.
Japanese Utility Model Application Publication No. 16,752/78 described an operating mechanism to enable shifting of operating lever even when the vehicle is running along a curved road. The operating lever can be operated in any running condition of the vehicle, and an actual changeover of the transfer unit is effected only after the vehicle begins to run straight, i.e. when the rotations of front and rear wheels becomes substantially the same. Thus, such a mechanism is called as waiting mechanism. Although each of the two known mechanisms improve operability of transfer units, other disadvantages are encountered when the both mechanisms are combined in one transfer unit.
The first mentioned mechanism has an interlock between two shift rods and a rocker lever which interengages with the shift rods to sequentially obtain by one operating lever the four positions, i.e. high speed two wheels drive, high speed four wheels drive, neutral, and low speed four wheels drive positions. When the waiting mechanism described in the second mentioned mechanism is combined with the shift rod of the first mentioned mechanism to effect shift between the four wheels and two wheels drive conditions, the interlock controls the movement of the shift rods despite actual engaging condition of the transfer unit, so that undesired engaging condition can occur. Namely, when the operating lever is shifted from the high speed two wheels drive condition to the low speed four wheels drive condition, this shift is effected through the high speed four wheels drive condition and the neutral condition. Further, when the waiting mechanism is in operation, and both shift rods move in accordance with the position of the operating lever, the transfer unit remains in the two wheels drive condition. Consequently, the operating lever is in the low speed four wheels drive condition while the actual transfer unit is in the low speed two wheels drive condition. Such a low speed two wheels drive condition is undesirable in that wheel racing may occur by an excessive unit power when the vehicle is running along muddy ground. Further, there may be applied too much torque to the drive elements, e.g., propeller shaft or differential gear, and resulting damages thereof may take place when the low speed two wheels drive condition is selected at a relatively high speed of the vehicle.